General Biology Exam Study Guide: Foundations of Life and Chemistry

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Definition of Life

What is Life?

Biologists define life by a set of characteristics that distinguish living organisms from non-living matter.

• Organization: Living things are composed of one or more cells, which are considered the basic units of life.

• Metabolism: All living things carry out chemical reactions to obtain and use energy.

• Homeostasis: The ability to maintain a stable internal environment.

• Growth and Development: Organisms grow and develop according to specific instructions coded in their DNA.

• Reproduction: The ability to produce new organisms, either sexually or asexually.

• Response to Stimuli: Living things respond to environmental changes.

• Evolution: Populations of living organisms evolve over generations.

Experimental Design

Variables and Controls

Scientific experiments are structured to test hypotheses by manipulating variables and using controls.

• Independent Variable: The factor that is changed or manipulated by the researcher.

• Dependent Variable: The factor that is measured or observed in response to changes in the independent variable.

• Control Group: The group that does not receive the experimental treatment, used for comparison.

• Constants: All other factors kept the same to ensure a fair test.

Atomic Structure and the Periodic Table

Atoms and Elements

Atoms are the basic units of matter, composed of protons, neutrons, and electrons. The periodic table organizes elements by atomic number and properties.

• Atomic Number: Number of protons in the nucleus of an atom.

• Atomic Mass: Sum of protons and neutrons.

• Valence Electrons: Electrons in the outermost shell, important for chemical bonding.

• Key Elements in Biology: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), and Sulfur (S).

Example: Carbon has 6 protons, 6 neutrons, and 6 electrons. Its atomic number is 6.

Chemical Bonding

Types of Bonds

Atoms combine to form molecules through different types of chemical bonds.

• Ionic Bonds: Formed when electrons are transferred from one atom to another, creating charged ions (e.g., NaCl).

• Covalent Bonds: Formed when atoms share pairs of electrons (e.g., H2O).

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., between water molecules).

Example: Table salt (NaCl) is formed by the ionic bond between sodium (Na+) and chloride (Cl-).

Single and Double Bonds; Stoichiometry

• Single Bond: One pair of electrons shared (e.g., H-H).

• Double Bond: Two pairs of electrons shared (e.g., O=O).

• Stoichiometry: The ratio of atoms in a molecule, important for understanding chemical reactions and molecular shapes.

Elements as Foundations of Biology

Major Elements

The most common elements in biological molecules are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N). These elements form the backbone of organic molecules.

• Carbon: Forms four covalent bonds, allowing for complex molecules.

• Hydrogen: Involved in energy transfer and structure.

• Oxygen: Essential for respiration and water.

• Nitrogen: Key component of amino acids and nucleic acids.

Importance of Carbon

Role in Biological Molecules

Carbon's ability to form four covalent bonds makes it uniquely suited to form the complex structures of life, including carbohydrates, lipids, proteins, and nucleic acids.

• Versatility: Can form chains, rings, and branched structures.

• Backbone of Organic Molecules: All major macromolecules are carbon-based.

Polarity of Molecules

Polarity and Water

Polarity refers to the distribution of electrical charge over the atoms in a molecule. Water is a polar molecule, meaning it has partial positive and negative charges.

• Polar Molecules: Have regions with slight electrical charges due to unequal sharing of electrons (e.g., H2O).

• Nonpolar Molecules: Electrons are shared equally (e.g., O2).

• Importance: Polarity affects solubility and interactions between molecules.

Water: Properties and Importance

Water's Role in Life

Water is essential for life due to its unique chemical and physical properties.

• Cohesion and Adhesion: Water molecules stick to each other and to other surfaces.

• High Specific Heat: Water can absorb a lot of heat before changing temperature.

• Solvent Properties: Many substances dissolve in water, facilitating chemical reactions.

• Ice Floats: Solid water is less dense than liquid water, allowing ice to float.

Example: Water's solvent properties are critical for transporting nutrients and waste in organisms.

pH and Acids/Bases

Understanding pH

pH measures the concentration of hydrogen ions (H+) in a solution, indicating its acidity or basicity.

• Acidic Solution: pH < 7, higher concentration of H+.

• Neutral Solution: pH = 7, equal concentrations of H+ and OH-.

• Basic Solution: pH > 7, higher concentration of OH-.

Formula:

$[H^+][OH^-] = 1 \times 10^{-14}$

Example: If [H+] = 1 x 10-7 M, then pH = 7 (neutral).

Functional Groups in Biological Molecules

Key Functional Groups

Functional groups are specific groups of atoms within molecules that have characteristic properties and chemical reactivity.

Functional Group	Structure	Example	Importance
Hydroxyl	-OH	Alcohols (e.g., ethanol)	Increases solubility in water
Carbonyl	>C=O	Aldehydes, ketones	Found in sugars
Carboxyl	-COOH	Amino acids, fatty acids	Acts as an acid
Amino	-NH2	Amino acids	Acts as a base
Sulfhydryl	-SH	Cysteine	Forms disulfide bonds in proteins
Phosphate	-PO4	ATP, nucleic acids	Energy transfer

Example: The carboxyl group (-COOH) gives amino acids their acidic properties.